Orthogonal Frequency-Division Multiple Access (OFDMA) is a multiple access method for sharing a radio frequency (RF) channel among multiple users. OFDMA uses an orthogonal frequency-division multiplexing (OFDM) digital modulation scheme to modulate information signals. OFDMA can be described as a combination of frequency domain and time domain multiple access. In OFDMA, a communication space is divided into a plurality of time slots, and each time slot is further divided into a number of frequency sub-channels each having at least one of its own sub-carriers. In OFDMA systems, both time and/or frequency resources are used to separate multiple user signals. Transmissions to/from multiple users are separated using time slots and sub-channels within each time slot such that users' signals can be separated in the time domain and/or in the frequency domain. Thus, in OFDMA, resources can be partitioned in the time-frequency space.
Recently, broadband wireless networks have been developed that implement OFDMA. For instance, IEEE 802.16 networks are one example. As used herein, “IEEE 802.16” refers to a set of IEEE Wireless LAN (WLAN) standards that govern broadband wireless access methods. IEEE 802.16 standards have been and are currently being developed by working group 16 of the IEEE local area network/metropolitan area network (LAN/MAN) Standards Committee (IEEE 802). Any of the IEEE standards or specifications referred to herein may be obtained at http://standards.ieee.org/getieee802/index.html or by contacting the IEEE at IEEE, 445 Hoes Lane, PO Box 1331, Piscataway, N.J. 08855-1331, USA. The Institute of Electrical and Electronics Engineers (IEEE) 802.16 Working Group on Broadband Wireless Access Standards is a unit of the IEEE 802 LAN/MAN Standards Committee that aims to prepare formal specifications to support the development and deployment of broadband Wireless Metropolitan Area Networks. In such 802.16 communication networks, communications signals between a base station and a station are modulated using OFDM. In one configuration, the OFDMA channel is split into a number of time slots. Each time slot is further divided into a number of frequency sub-channels (e.g., one 70 MHz wide time slot can be divided into fourteen sub-channels each being five MHz wide).